Process of preparing acetaldehyde.



UNITED STATES PATENT OFFICE.

ERICH BAUM AND MARTIN MUG-DAN, OF NUREMBERG, GERMANY, ASSIGNORS T0 CON-SORTIUM FI l'R ELEKTROCHEMISCHE INDUSTRIE G. M. B. H., 01? NUREMBERG,

Patented Ma 12,1914.

GERMANY.

PROCESS OF PREPARING ACETALDEHYDE.

1 ,O96,667 Specification of Letters Patent.

No Drawing. Application filed March 18, 1913.

Serial No. 755,238. i

the latter upon a strong solution of sulfuric acid containing mercuricoxid (see for example Erdmann and Kothner, Zeitschrift f. zlnorg-OhernieXVIII S. 55). Difficulty has been experienced in working on these linessince a considerable part of the acetaldehyde which has been formed istrans formed into condensation products 'aldol, crotonic aldehyde, etc.)owing to the high concentration of acid which was considered to beindispensable.

According to the present invention the absorption of acetylene and itstransformation into acetaldehyde is effected in the presence of oxid ofmercury and sulfuric acid by limiting the acid content and by workinoata temperature above the temperature of distillation of the acetaldehyde.It. has been hitherto considered necessary in the formation ofacetaldehyde from acetylene, mercuric oxid and sulfuric acid to make alarge addition of acid. The present invention depends on the contrary onthe fact that the amount of acid should only be such that the totalquantity in the reaction liquid should be at most 60 grs. SO, per 1000grs. water. Thus in the present process ,it is essential to limit theamount of S0, to at most 60 grs. SO per liter and moreover to operate ata temperature at which the aldehyde which is formed is evolved in thestate of vapor. In this way a smooth formation of the acetaldehyde isattained and at the same time the recovery of the mercury which hasseparated out "in the process is facilitated to an extraordinaryextent.The formation of condensation and transformation products ofacetaldehyde is almost entirely avoided. The mercury collects at the bottom of the reaction vessel in the form of a metallic regulus and whenthis has been oxidized it can readily be introduced into the processagain in an economical manner, whereas in the known process in whichlarge general remark has been made that in the V preparation ofaeetaldchyde from acetylene by means of solutions of mercury salts andsulfuric acid, the concentration of the sulfuric acid and thetemperature of reaction are dependent on one another in such manner thatlower temperatures should be employed at higher concentration and thereverse. It is further suggested when using 20% sulfuric acid theintroduction of acetylene takes place at 40 and the aldehyde which isformed is distilled off at about 70. The only example given in theFrench patent for working with dilute acid (example 3 page 3) is one inwhich 25% acid is used at 40 to 45, and the isolation of the alde-- hydewhich is formed must then be effected by laborious distillation invacuo. Thus it is not possible either under these conditions or whenusing 20% acid to introduce acetylene continuously in the mannerprescribed by us, whereby we obtain pure aldehyde forthwith in thedistillate with simultaneous formation of clean mercury, and without theformation of by-products. Thus from the results given in the Frenchpatent itcould not have been foreseen that it is possible at the muchlower concentrations chosen by us (at most 60 grams SO, per 1000 gramsof water) to introduce acetylene continuously and to distil off verypure aldehyde without further complications, and also to obtain themercury again as a clean metallic regulus, thus making an importantadvance beyond the process given in this patent.

Example: 1750 grams mercuric oxid are added to 24 liters 33, 70 sulfuricacid and acetylene is introduced with vigorous stirring and with heatingto about 70 to 80. Within thirty hours 5 to 6 kilograms of almost pureacetaldehyde condense in the worm condenser connected with the reactionapparatus, the yield being almost theoretical calculated on theacetylene. The mercury is found at the endat the bottom of Ill) theliquid as a clean metallic regulus. The liquid is almost water-clear andfree from resin and dissolved mercury.

The mercury may be transformed again into mercuric sulfate by dissolvingin concentrated sulfuric acid with heating, and again employed ascatalyst. However, in this method of regenerating the catalyst, largequantities of sulfuric acid will be consumed and thus the operationwould be tedious and unpleasant, owing to the evolution of sulfurdi-oxid. We overcome this difficulty by oxidizing the mercuryelectrolytically. For this purpose we employ for instance an alkalineelectrolyte and we may use with advantage a low percentage solution ofcaustic soda beneath which the mercury is placed as anode, while thecathode placed there-over is conveniently of iron and provided withopenings for leading off thehydrogen. The mercury anode then soonbecomes covered with a dark coating of mercurous oxid, which is to becontinuously removed during the electrolysis by raking or by blowingelectrolyte thereon or in any other suitable manner, in order to obtainfavorable conditions of potential. The mercurous oxid so obtained whichstill contains metallic mercury and mercuric oxid is treated with adilute sulfuric acid solution containing less than about grams SO perliter and again treated With acetylene While hot. The fact that in thismethod of working only mercurous salt is present from the beginning,possibly in presence of metallic mercury, in no way influences thecourse of the reaction. However, it is known. to transform mercury intomercuric oxid or sulfate by the electrolytic method (of, for exampleBritish Patent N 0. 28400 of 1903, and Severin Toute la Ohz'mieillz'mmle par ZElectrz'cz't, 1908, page 645). This reaction has hithertofound no application in connection with the preparation of acetaldehydefrom acetylene. It could not have been foretold that the product ofelectrolysis mainly consisting of mercurous oxid or of mercuric oxidwith metallic mercury, which on solution in sulfuric acid is transformedto mercurous sulfate wholly or'to a very large extent, could be employedin the present process and that indeed the mer curous compound is almostentirely aseffective for the hydration of the acetylene as theequivalent quantity of mercuric salt.

The employment of the electrolytic regeneration of the oxid of mercuryemployed in combination with the present process of preparing aldehydecreates a cyclic process and. thereby considerably increases thetechnical value of this method of preparing aldehyde.

In the claims We shall use the Words sulfate of mercury as mcludmgeither mercuric sulfate or mercurous sulfate or a mixture of both or abody obtained by treating mercuric oxid or mercurous oxid or a mixtureboth, with sulfuric acid.

e declare that what we claim is 1. The process for the manufacture ofacetaldehyde which comprises causing acetylene to interact with asolution of sulfuric acid containing sulfate of mercury as catalyst at atemperature at which acetaldehyde distils from said solution and at aconcentration of acid not higher than 6%.

2. The process for the manufacture of acetaldehyde which comprisescausing acetylene to interact with a solution of sulfuric acidcontaining sulfate of mercury as catalyst ata temperature 70-S0 C. andat a concentration of acid not higher than 6%.

3. The process for the manufacture of acetaldehyde which comprisescontinuously causing acetylene to interact with a solution of sulfate ofmercury as catalyst and not more than 6% of sulfuric acid, andsimultaneously distilling off the acct-aldehyde thus formed.

4. The process for the manufacture of acetaldehyde which comprisescausing acetylcne to interact with a solution of sulfuric acid of aconcentration not higher than 6% and containing sulfate of mercury ascatalyst, and heating the solution to such a temperature that theacetaldehyde thus formed distils off.

5. The process for the manufact-ure of acetaldehyde which comprisescausing acetylene to interact with a solution of sulfuric acidcontaining mercurous sulfate as catalyst at a temperature at whichacetaldehyde disti'ls from said solution and at a concentra tion of acidnot higher than 6%.

6. The cyclic process for thelmanufacture of acetaldehyde whichcomprises causing acetylene to interact with a solution of sulfuric acidat a concentration not higher than 6%, containing a catalyst consistingsubstantially of mercurous sulfateat a temperature at which acetaldehydedistils from said solution, and re-oxidizing the mercury so formed byanodic oxidation introducing said oxidation product into sulfuric acidand again causing said solution to interact with acetylene.

In testimony whereof We aflix our signatures in presence of twowitnesses.

DR. ERICH BAUM. DR. MARTIN ll IUGDAN.

Witnesses: ADAM Krsorm,

GEoRG SErrz.

